[infinispan-dev] Design change in Infinispan Query

[Sanne Grinovero]

Up this: it was proposed again today ad a face to face meeting.
Apparently multiple parties have been asking to be able to run
cross-cache queries.

Sanne

On 11 April 2012 12:47, Emmanuel Bernard <emmanuel at hibernate.org> wrote:
>
> On 10 avr. 2012, at 19:10, Sanne Grinovero wrote:
>
>> Hello all,
>> currently Infinispan Query is an interceptor registering on the
>> specific Cache instance which has indexing enabled; one such
>> interceptor is doing all what it needs to do in the sole scope of the
>> cache it was registered in.
>>
>> If you enable indexing - for example - on 3 different caches, there
>> will be 3 different Hibernate Search engines started in background,
>> and they are all unaware of each other.
>>
>> After some design discussions with Ales for CapeDwarf, but also
>> calling attention on something that bothered me since some time, I'd
>> evaluate the option to have a single Hibernate Search Engine
>> registered in the CacheManager, and have it shared across indexed
>> caches.
>>
>> Current design limitations:
>>
>>  A- If they are all configured to use the same base directory to
>> store indexes, and happen to have same-named indexes, they'll share
>> the index without being aware of each other. This is going to break
>> unless the user configures some tricky parameters, and even so
>> performance won't be great: instances will lock each other out, or at
>> best write in alternate turns.
>>  B- The search engine isn't particularly "heavy", still it would be
>> nice to share some components and internal services.
>>  C- Configuration details which need some care - like injecting a
>> JGroups channel for clustering - needs to be done right isolating each
>> instance (so large parts of configuration would be quite similar but
>> not totally equal)
>>  D- Incoming messages into a JGroups Receiver need to be routed not
>> only among indexes, but also among Engine instances. This prevents
>> Query to reuse code from Hibernate Search.
>>
>> Problems with a unified Hibernate Search Engine:
>>
>>   1#- Isolation of types / indexes. If the same indexed class is
>> stored in different (indexed) caches, they'll share the same index. Is
>> it a problem? I'm tempted to consider this a good thing, but wonder if
>> it would surprise some users. Would you expect that?
>
> I would not expect that. Unicity in Hibernate Search is not defined per identity but per class + provided id.
> I can see people reusing the same class as partial DTO and willing to index that. I can even see people
> using the Hibernate Search programmatic API to index the "DTO" stored in cache 2 differently than the
> domain class stored in cache 1.
> I can concede that I am pushing a bit the use case towards bad-ish design approaches.
>
>>   2#- configuration format overhaul: indexing options won't be set on
>> the cache section but in the global section. I'm looking forward to
>> use the schema extensions anyway to provide a better configuration
>> experience than the current <properties />.
>>   3#- Assuming 1# is fine, when a search hit is found I'd need to be
>> able to figure out from which cache the value should be loaded.
>>      3#A  we could have the cache name encoded in the index, as part
>> of the identifier: {PK,cacheName}
>>      3#B  we actually shard the index, keeping a physically separate
>> index per cache. This would mean searching on the joint index view but
>> extracting hits from specific indexes to keep track of "which index"..
>> I think we can do that but it's definitely tricky.
>>
>> It's likely easier to keep indexed values from different caches in
>> different indexes. that would mean to reject #1 and mess with the user
>> defined index name, to add for example the cache name to the user
>> defined string.
>>
>> Any comment?
>>
>> Cheers,
>> Sanne
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>
>
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